The injection of fluidic materials into body tissue may be performed in a number of different medical procedures. In the field of ophthalmology, for example, intraocular injections may be administered for many reasons. Some of these reasons include: (1) the injection of antibodies to treat endothalmitis or prevent its onset; (2) the injection of Transforming Growth Factor Beta (TGFB) or other growth factors to treat macular disorders; (3) the injection of Tissue Plasminogen Activator (tPA) into the subretinal space to dissolve blood clots; (4) the injection of liquids and gases into the subretinal space to facilitate subretinal surgery; (5) the injection of viscoelastic substances to dissect preretinal membranes; and (6) the injection of gases into the vitreous cavity for pneumatic retinal pexy.
When intraocular injections are administered, the surgeon must control one or more of the following: injection rate, total volume administered, and location of the injected substance. The case of viscodissection is described to illustrate these requirements.
Viscodissection is a technique where preretinal membranes are hydraulically separated from the retina using a viscoelastic substance. This substance, which typically is sodium hyaluranate is injected between the membrane and the retina using a syringe and a small gage bent needle. Many surgeons find it difficult to hold the needle tip steady while they inject the fluid. As should be understood, inadvertent motion of the needle can cause damage to the retina and other surrounding tissues. Further, injecting too much fluid between the membrane and the retina, or injecting the fluid too fast, can also cause retinal damage which could lead to a retinal detachment.
A syringe adapter device which uses pneumatic energy to deliver the viscoelastic material has been previously designed. In this regard, the plunger of this previously designed device is driven by pneumatic pressure instead of finger pressure, which mitigates some of the positioning problems described above. Additionally, the pneumatic pressure source also affords good control of the volume delivered and the injection rate, providing the following factors are held constant: (1) the size of the syringe and the materials used in its construction; (2) the size, shape and material used for the plunger seal; (3) the inside diameter and inside surface finish of the injection needle; (4) the overall geometry of the injection needle; (5) the viscosity of the injected fluid and how it varies during the injection process; and (6) the temperature characteristics of the fluid and of the syringe.
A number of syringe adapters and pneumatic pressures sources are currently available, and these devices represent significant improvement over the hand-operated syringes for injecting a variety of substances. However, due to the variables listed above, these devices often cannot meet the requirements of the surgeons for precision. As will be appreciated, the volume delivered and the rate of injection are still dependent on the alertness, skill, and the responsiveness of the operator, and on the physical properties of the fluid. Accordingly, a need has arisen for a device for injection of fluidic materials into body tissue which will deliver a user-settable volume of fluid; will inject fluids at a rate precisely controlled by the operating physician; and will further minimize the risk of tissue damage that could result from a manually operated syringe.